I think there's an issue with safely encoding values of the Go type int on 64-bit systems. The type can contain values up to math.MaxInt64, while only values up to math.MaxInt32 can be safely encoded in the Avro type int. The type could safely get encoded into long, but the library doesn't support that.

You can find a reproducible test case here: https://gist.github.com/lovromazgon/50ecf204e65f7d1ad080fbd0fa7d52fb

The test tries to encode and decode a Go value of type int containing 2147483648 (i.e. math.MaxInt32 1) with two schemas:

• with schema int it succeeds, but the decoded value doesn't match (overflow)
• with schema long it fails because int is unsupported for Avro long

=== RUN   TestHamba_Int
    hamba_test.go:23: expected 2147483648, got -2147483648
    hamba_test.go:30: unexpected error: failed to encode: avro: int is unsupported for Avro long

The first case is a possible footgun, it's debatable if you want to add an option for the encoder to be "strict" and disable the support for encoding values of Go type int into Avro type int.

I personally care more about the second case, encoding a Go int into the Avro type long should work.

Let me know what you think, I can try to work on this and open a PR with a fix.

Possibly related to #59.